Alantolactone (I) and isoalantolactone (II) were separated from the root of Inula helenium. When I or II were reacted with cyclopentadiene (III), spiro(2.4)-4,6-heptadiene (IV), furan, anthracene and acrylaldehyde, the Diels-Alder reaction only occurred with III or IV. The configurations of the main addition products were determine by X-ray diffraction and high resoln. NMR.

Key words: LACTONES, SESQUITERPENE, PROPENAL, X-RAY DIFFRACTION ANALYSIS, NMR SPECTROMETRY, CYCLOPENTADIENE, ANTHRACENE, CONJUGATED DOUBLE BOND COMPOUNDS, DIENE SYNTHESIS, CONFIGURATION